David Fleetham / Florida manatee (Trichechus manatus latirostris) at Three Sisters Spring in Crystal River, Florida, USA.

David Fleetham / Florida Manatee (Trichechus manatus latirostris), Three Sisters Spring, Crystal River, Florida, USA. National Wildlife Federation Photo Contest Grand Prize WINNER 2010.

Yva Momatiuk & John Eastcott / Ripples on white gypsum sand dunes, White Sands National Park, New Mexico

Floris van Breugel / Black and white photograph of Ice crystals up to 12 inches long along a small creek in a remote valley, Brooks Range, Gates of the Arctic National Park, Alaska, August 2014.

Tim Fitzharris / West Indian Manatee (Trichechus manatus) mother and calf, Crystal River, Florida

Franco Banfi / Nudibranch (Janolus cristatus) Vela Luka, Korcula Island, Croatia, Adriatic Sea, Mediterranean

Alex Mustard / Trees and sky photographed at dawn through the surface of Three Sisters Spring, Crystal River, Florida, United States of America.

Franco Banfi,Franco Banfi / Ocean Sunfish (Mola Mola) with Longfinned bannerfish (Heniochus acuminatus) Crystal Bay, Nusa Penida, Bali Island, Indonesia, Pacific Ocean

Gavin Hellier / Aerial view of the famous Blue Lagoon and Belcekiz beach along the 'Turquoise' coast, Oludeniz near Fethiye, Mediterrean Coast, Turkey 2008

Gavin Hellier / Aerial view of the famous Blue Lagoon and Belcekiz beach along the 'Turquoise' coast, Oludeniz near Fethiye, Mediterrean Coast, Turkey 2008

Cheryl-Samantha Owen / Blacktip reef sharks (Carcharhinus melanopterus) swimming in shallow crystal clear water, Aldabra Atoll, Seychelles, Indian Ocean

Cheryl-Samantha Owen / Blacktip reef sharks (Carcharhinus melanopterus) swimming in shallow crystal clear water, Aldabra Atoll, Seychelles, Indian Ocean